Physical Media and Channels

Abstract

Physical Media and ChannelsUltimately the design of a digital communication system depends on the properties of the channel. The channel is typically a part of the digital communication system that we cannot change. Some channels are simply a physical medium, such as a wire pair or optical fiber. On the other hand, the radio channel is part of the electromagnetic spectrum, which is divided by government regulatory bodies into bandlimited radio channels that occupy disjoint frequency bands. In this book we do not consider the design of the transducers, such as antennas, lasers, and photodetectors, and hence we consider them part of the channel. Some channels, notably the telephone channel, are actually composites of multiple transmission subsystems. Such composite channels derive their characteristics from the properties of the underlying subsystems.Section 18.1 discusses composite channels. Sections 18.2 through 18.4 review the characteristics of the most common channels used for digital communication, including the transmission line (wire pair or coaxial cable), optical fiber, and microwave radio (satellite, point-to-point and mobile terrestrial radio). Section 18.5 discusses the composite voiceband telephone channel, which is often used for voiceband data transmission. Finally, Section 18.6discusses magnetic recording of digital data, as used in tape and disk drives, which has characteristics similar in many ways to the other channels discussed.

Experimental Study of Plane Spiral OAM Mode-Group Based MIMO Communications

“…is the complex additive white Gaussian noise vector [27] at the receiving end; and H = [h mn ] ∈ C N ×N is the complex transfer matrix that consists of several transfer functions. Here, H can be either H MIMO or H MG .…”

“…In the case of the QPSK transmission, as far as the test results are concerned, when ∆l e is 5 or 7, the MG-MIMO system can reach a raw BER level of 3.8 × 10 −3 , which is a level allowing extremely low error rates in virtue of efficient forward error correction (FEC) codes [27]. Benefiting from the lower sub-channel correlation, the multiplexing of MG 7 and MG 8 can reach the FEC limit at a lower SNR of about 26 dB, and the multiplexing of MG 5 and MG 6 needs a 28 dB SNR to reach the same limit.…”

The inherent uncertainty of temporal networks is a true challenge for control

“…To delve into this regime, we should take into account that all real world systems that can be modeled as dynamical network are characterized by time scales. Those of digital communication networks 18 , for instance, are determined by the dynamical flow of the data packets, whereas those of epidemic processes 19 depend on the specific infection taking place, and can range from few days to months 20 . For a linear network, and thus for each of our snapshots, the time scale is related to the eigenvalues of .…”

BLE or IEEE 802.15.4: Which Home IoT Communication Solution is more Energy-Efficient?

“…Yet, in terms of wireless performance, IEEE 802.15.4 is expected to perform better. Due to the lower bandwidth (IEEE 802.15.4 operates at 256 Kbps, whereas BLE operates at 1 Mbps), IEEE 802.15.4 has a 6 dB better sensitivity at the same operating temperature [11].…”